The present invention is directed to a process for casting railroad ties and the like and for apparatus employed in said process. More specifically, the present invention is directed to the casting of concrete with maximum mold utility.
Conventional wooden railroad ties, for technical and economic reasons, are being progressively replaced by ties made of reinforced concrete. The concrete ties have a longer useful life and make possible higher train speeds. Such concrete ties are generally molded and prestressed.
Prestressing requires that the concrete product remain in the mold during curing. Once sufficiently cured, the prestressing members can be released from the mold and the tie removed. In such an operation where a large number of ties are to be produced economically, a substantial number of molds are required. The requirement for a large number of molds results from the need, under present systems, to retain the prestressing tendons tensioned in the mold until sufficient strength is exhibited by the concrete to retain them in a tensioned condition.
Efforts have been made, including accelerated curing cycles, generally carried out in boxes or tunnels heated with steam, to improve the molding cycle. Notwithstanding such efforts, generally molds employed in such processes cannot be cycled more than once or twice during twenty-four (24) hours. Naturally, capital expenses as well as manufacturing complexities can be reduced with increased mold utility.